How is it that tears fill my eyes before I even begin to write to you? I can only guess it’s because you hold the key to my heart like no other person ever will. You — my precious, precocious and beautiful son — are my heart.

Now I can imagine parents out there who don’t have a child with a life-limiting illness may read this letter and say, “Oh, this is the way we feel about our child/children, too.” But Declan, I can assure you it’s different. As you know, my wise 7-year-old son (with an old soul), this journey we are on changes everything about life. Everything.

From the time you were an infant and I would lie you next to your big brother, Brendan, you’d smile up at him in a sort of tender recognition. As the months turned into years, your bond with him — your unconditional love for him — has made me stop in my tracks in awe. Even now, I’m smiling as I type this, remembering you said something to me last month that I will always hold dear.

You were matter of fact, but you were also clearly keeping my feelings in mind. You said, “Mom, I hope it’s OK, but I love my brother more than anyone in the world — even more than I love you.” How you melted my heart at that moment! Yes, my love, it’s absolutely OK to love him more than you love me. Please, please do. Because as you know, as we have gently discussed on far too many occasions, your brother won’t be with us in this life for very long.

A couple of months ago when Brendan was in the hospital for 19 days, I bought you a mood ring at a local shop. Must be the old hippie in me coming out, right? I will never forget later that afternoon when we were hanging out in Brendan’s hospital room, you walked up to him, took off your new mood ring and placed it on his finger. You said, “Here, Brenny, this will make you feel better because it’s on the happy color now.” Have I told you just how much you amaze me, Declan? You have the most compassionate heart of any child I know.

Last week, you stood by your brother’s side as his body seized out of control. His body convulsing, his lungs barely breathing, his skin losing the warmer colors and turning to blue. You said, “Come on Brendan, we’re right here, it’s OK.”

And you held his hand.And you laid your hand on his head.And you said how much you love him.

I saw every single second of it while I stood right next to you as I monitored your big brother.You have seen paramedics rush into the house at midnight to tend to your brother. You have seen your brother taken by an ambulance as its lights and sirens went off while we followed behind. You have seen tubes and masks and IV lines in your brother’s hands and feet often all at the same time. You have been to so many X-ray appointments for Brendan that you now just walk behind the screen and hang out with the X-ray tech, knowing that’s just where to go. (And that there is usually a great supply of stickers to be found there!)

You have sat with me, quietly, when I simply couldn’t hide my tears no matter how damn hard I tried. You have taken on a sort of caretaker role unknowingly, but so acceptingly, and you’re innately mastering it.

I know, my sweet and tender child, that much of this is not fair for you. So many times in your life you have already had to sacrifice by not being able to go where you would like or when you would like because Brendan simply wasn’t able for it. So many times you have cried because of those sacrifices. But hear this promise, Declan, and let it soak in: Everything you miss out on, everything you do for your brother and for me and every loving word you say to your brother, it all stays with me. It is emblazoned upon my mind, my heart and my soul, and I promise you it will all be made good. For you are growing into the kind of man who will make the world a truly better place. You will impart reason, compassion, sensitivity and great love in whatever you choose to do.

My promise to you is that I will never, ever let the struggles of this journey turn you away from the beauty that you’re learning on this journey. You will be all that you can be. And that, my son, is everything.